1. Field of the Invention
The present invention relates to ceramic articles such as ceramic heaters, ceramic static chucks or the like.
2. Related Art Statement
In a field of semiconductor apparatuses such as etching apparatuses, chemical vapor deposition apparatuses, or the like, so-called "stainless heaters" and heaters of indirect heating type have been generally used. However, these heat sources have posed problems such that particles generated by action of halogenous corrosive gases reduce heating efficiency. In order to solve the problems, the inventors proposed a ceramic heater in which a wire made of a metal having a high melting point is embedded in a dense ceramic disc-shaped substrate. This wire is in a spirally-coiled shape within the disc-shaped substrate and connected at both ends thereof with terminals. It has been found that this ceramic heater has excellent characteristics particularly for the manufacture of semiconductors.
In order to manufacture the ceramic heater mentioned above, a wire or filament made of a metal having a high melting point is wound up into a convolution, both ends of which are connected with terminals, respectively. On the other hand, ceramic powders are charged into a press-molding machine and preformed to have a certain extent of hardness. In this case, a continuous recess or groove is provided along a predetermined planar pattern on the surface of the preformed body. Then, the convolution is accommodated in the recess and covered with the ceramic powder. Then, the ceramic powders are subjected to a uniaxial pressure molding to form a disc-shaped molded body which is then sintered by a hot-pressing method.
The reason for making a shape of the ceramic heaters to a disc-shape is as follows. In the known stainless heater, a heating plane for a semiconductor wafer is largely separated from the terminals of a resistance heating element, and a cable for power supply is connected with the terminals at an outer portion from a container of the semiconductor manufacturing apparatus. Generally, a heating plane shows a high temperature and is exposed to a corrosive atmosphere. However, the connection portion between the terminals and the cable does not become a high temperature and also is not exposed to a corrosive atmosphere. On the contrary, in the case of manufacturing the ceramic heaters, since the resistance heating element is arranged in the ceramic powders and is molded, it is necessary to use a simple molded shape such as a disc-shape or the like from a manufacturing point of view. Also in the sintering step, since the molded body is subjected to a hot-press sintering, it is preferred to use a simple molded shape such as a disc-shape or the like. Moreover, a sintered deformation layer as shown by a black portion is generated on a surface of the sintered body after the sintering, and this sintered deformation layer must be removed by a machining operation. In this case, it is necessary to use a diamond whetstone or the like. Therefore, if the shape of the sintered body is complicated, the cost for this machining operation becomes extremely large. In this manner, in the ceramic heater in which the resistance heating element is embedded, it is necessary to use a simple shape such as a disc-shape or the like due to a difficulty on the manufacturing. Therefore, it is very difficult to arrange the terminals of the ceramic heater outside of the container of the semiconductor manufacturing apparatus from the structural point of view. Consequently, in the ceramic heater in which the resistance heating element is embedded, the terminals thereof are inevitably exposed to a corrosive gas having a high temperature.
In order to solve this problem, the applicant disclosed, in Japanese Patent Laid-open Publication No. 4-87,179 (JP-A-4-87,179), a method of connecting the terminals of the ceramic heater with the power supply member in a heat resistive and corrosion resistive manner. In this case, it is necessary to make a diameter of the terminals large and to connect end portions of the resistance heating element with the terminals.
As for the connecting method, there is a method such that the end portions of the resistance heating element are inserted to caulking portions formed at the terminals, and the caulking portions are caulked to fix the end portions to the terminals. FIG. 1 is a partial cross sectional view showing a connection portion between a terminal 12 and a resistance heating element 2 in the ceramic heater mentioned above. In FIG. 1, the resistance heating element 2 is shown by a front view for a convenience of understanding. In this embodiment, the resistance heating element 2 and the terminal 12 are embedded in a disc-shaped substrate 1. Two principal planes 1a and 1b are arranged to the disc-shaped substrate 1. A main body 12b of the terminal 12 has an exposed plane 12a exposed to a side of the principal plane 1b. Moreover, the resistance heating element 2 is made of a coiled-spring convolution. A numeral 5 shows a respective coil constituting the convolution. A linear portion 30 arranged at an end portion of the coil 5 is inserted into a cylindrical projection portion 12c of the terminal 12. The cylindrical projection portion 12c is caulked to connect the resistance heating element 2 with the terminal 12 in such a manner that an end portion 13 of the linear portion 30 is inserted in an inner portion 22 of the cylindrical projection portion 12c.